In the treatment of certain disorders occurring in body cavities or ducts frequently heat is supplied, so called hyperthermia. It has for example been known for a long time that so called menorrhagia, i.e. a disorderly condition, characterized by strong menstrual bleeding, can be cured by heat destruction of the so called endometrium, which is a mucosal membrane lining the uterus cavity. Said cavity has in a front view a triangular shape with a base facing upward. The cervix canal opens in the lower triangle apex and the fallopian tubes in the upper, counter-positioned triangle apexes.
Since access to the cavity can take place only through the cervical canal which is narrow it has inter alia been suggested to use catheters having an expandable bladder connected to the distal end of the catheter. When treating menorrhagia the front end of the catheter comprising the unexpanded bladder is inserted into the uterus cavity via vagina and cervix.
The bladder is then expanded by means of the supply of a pressure medium, for example a liquid, via a canal centrally placed in the catheter from a liquid container, whereby the usually rather flat cavity is widened so that the balloon will engage the major part of the surface of the endometrium. Clinical tests have shown that it is important for a successful result of the treatment that the entire endometrium is heated with the exception of the cervical area and that the pressure is maintained at a relatively high level, suitably up to 160-200 mm Hg, so as to improve heat convection, partly in view of the fact that the circulation of blood in the tissue will be reduced. On the other hand the pressure should not exceed about 250-300 mm Hg in view of risk of rupture of the tissue.
The pressure medium is then heated by heat-releasing means, for example an electric resistance element, to a suitable temperature, for example between 70 and 90.degree. C. When the temperature has been reached the treatment starts and is directed to necrotizing the endometrium under heat and pressure to a depth of about 5-7 mm. Normally, a period of treatment of between 6 and 15 minutes is sufficient.
Expandable balloon catheters for the heat treatment of menorrhagia are described for example in U.S. Pat. No. 4,949,718 (Neuwirth et al), U.S. Pat. No. 5,693,080 (Wallsten), WO94/21202 (Wallsten et al), WO96/26695 (Claren et al), U.S. Pat. No. 5,084,044 (Quint).
Since the cervical canal normally has a diameter of only 3-5 mm the treatment must as a rule be preceded by dilatation with a so called Hegar dilator in order to allow for passage of the balloon catheter. The dilatation is painful and the degree of pain is often related to the extent of dilatation. For certain catheters appearing on the market a dilatation to 8-9 mm must be made which increases the requirement for anaesthesia.
Therefore, it is highly desirable to design such catheters with a small diameter in order to reduce the degree of dilatation and to facilitate insertion. On the other hand the cervical canal is sensitive to the effect of heat. Heating can result in the formation of stenosis completely obstructing the canal. Therefore, the canal has to be protected by heat insulation surrounding the canal. Since the efficiency of the heat insulation is largely dependent on the radial thickness thereof one has to compromise between the wish for a small catheter diameter and an efficient heat insulation.
In U.S. Pat. No. 4,949,718 and U.S. Pat. No. 5,693,080 balloon catheters are described where the heat-releasing means is centrally positioned in the balloon. In the first case it is constituted by an electric resistance coil and in the other case a non-linear electric resistance of so called PTC type.
In the latter case forced circulation is generated within the balloon by exerting pulsation on the heating medium in the inlet passage, whereas no circulation is used in the device according to U.S. Pat. No. 4,949,718. In the devices described in WO94/21202, WO96/26695 and U.S. Pat. No. 5,084,044 the liquid is circulated through an inlet passage and an outlet passage between the balloon and an external heat source.
Generally, one can say that devices using a circulating liquid result in an effective and even heat transfer and thereby good result of treatment. On the other hand it is important that the expanded balloon is adapted to the cavity surface to be treated. Such devices also require efficient insulation in the cervical area in view of the large amount of hot liquid that circulates through the supply and discharge conduits.
The size of the uterus cavity varies greatly between different patients. The length or depth of the cavity is usually between about 40 mm and 80 mm and the length of the cervical canal varies between about 20 and 40 mm. The cavity volume as extended by a balloon or bladder is between about 3 and 60 ml.
A problem associated with devices for heat destruction of the endometrium using balloon catheters is the large variation of volumes and cavity depths. As previously indicated it is important that the balloon or bladder engages the major part of the endometrium surface and that it can be expanded outwardly towards the fallopian corners. On the other hand the cervical canal and its opening into the cavity, the so called istmus region, must be protected from influence by heat.
This problem has been solved in said U.S. Pat. No. 4,949,718 in that the catheter has a scale graduation by which a suitable insertion depth can be selected. Since the proximal end of the bladder is attached to the distal end of the catheter, whereas the distal end of the bladder is free, the balloon will move axially forward when expanded so as to be brought into contact with the endometrium (FIGS. 1, 2, 7 and claim 1). The intention is that the operator choses the insertion depth so that the attachment of the bladder to the catheter is forward of the cervix so as to prevent all contact between the bladder and the cervical canal.
This device is associated with several drawbacks. Since the distal end of the catheter moves freely somewhere in the middle of the cavity, and since the balloon or bladder when expanded exerts a certain counter pressure, it is difficult for the operator to check the correct position, whereby there is risk for heat damages on the cervix. Furthermore, there is risk that the catheter points obliquely so as to perforate the cavity wall or so as to cause burn damage in view of contact between the hot resistance element and the wall. Another disadvantage is that the proximal part of the balloon also can expand axially rearwardly causing risk for heat damage at the opening of the cervical canal into the cavity.
In the devices according to the other references the balloon is attached to the cavity both in its proximal and in its distal part. When inserted the catheter is moved so as to reach the cavity fundus. In view of the fact that the catheter is attached at both ends thereof it will in its expansion automatically be centered to the center of the cavity.
The balloons of the device according to WO94/21202 are constituted by for example pre-shaped balloons. The pre-shaped balloons or bladders are designed with the wide part placed distally. Such balloons are, accordingly, adapted to the shape of the cavity and would have the advantage that they will have a better reach when expanded out into the fallopian corners. The pre-shaped balloons are folded around the catheter before insertion, which is a disadvantage in view of a increase of the diameter.
In a particular embodiment the pre-shaped balloon ban be axially stretched so that the diameter will be reduced and insertion facilitated. After the insertion of the catheter the balloon is reverted to its original position so that it can completely fill the uterus cavity.
In WO96/26695 there is described a balloon catheter which is connected to an external heat source and where the liquid is circulated between the balloon and an external liquid container via passages or canals. The catheter is constituted by a tube which is closed at its distal end. The distal section of the tube is surrounded by an elastic piece of hose of silicon rubber which in an unexpanded state adheres to the exterior surface of the tube and is attached to the tube at both ends thereof. With supply of liquid the hose piece will be extended to a balloon.
A sleeve is arranged around the catheter tube and is axially displacable thereon. Near its distal end the sleeve has an exterior shoulder. With retracted sleeve the catheter is inserted and the sleeve is then pushed forward until engaging the cavity entrance, the so called sound measure constituted by the sum of the cavity depth and the cervical canal length can be determined from a scale. The expandable part of the hose piece, i.e. the length of the balloon, can thus be adapted to the cavity depth of the uterus.
However, this device is associated with several disadvantages. As a balloon material there can only be used a tubular piece so as to enable displacement of the sleeve. Furthermore, the displacable sleeve with the necessary play between the sleeve and the catheter tube results in a considerable increase of the diameter of the catheter which, as previously indicated, is not desirable. From the description of said patent application it is not clear how the necessary heat insulation of the catheter part positioned in the cervical canal is arranged. It is, however, obvious, that in view of the necessary gap or play blood and body liquid can enter and impair the insulation.
A further disadvantage is that the length of the balloon according to this device is determined by the sound measure. Since the latter can also vary from individual to individual as introductorily mentioned the length of the balloon will not always match the cavity depth.
Except for WO96/26695 all devices mentioned above contain no means for adjusting the balloon length to match different cavity depths.